Stripping compositions containing strong chemical agents; which are corrosive to the eyes, the skin, the respiratory tract, and some metals, for example, phenol, in combination with methylene chloride are presently in use for stripping paint from commercial and military aircraft. These compositions cause the paint to swell and loosen from the substrate. The common paint stripper activators used (in particular, phenol) are highly toxic, caustic, and/or deleterious.
More specifically, paint strippers typically contain solvents, co-solvents, activators, evaporation retardants, thickeners, wetting agents, emulsifiers, and corrosion inhibitors. The most important role of a solvent in a paint stripper is its diffusivity, which was found through the paint stripping mechanism study performed under the Strategic Environmental Research and Development Program (SERDP) Project Number WP-1682. Other roles of solvents include swelling target paints and delivering activators to the interfaces of paints and substrates. Co-solvents are commonly used to increase swelling of the target paint. Activators are believed to break or weaken the bonds between paints and substrates as well as chemical and physical bonds in polymers. Common activators used in paint stripper formulations are phenol, acids, bases, peroxides, and water. Phenol is a solid at ambient temperature and slightly acidic in aqueous solution. Even though phenol is acidic, no evidence of its corrosiveness on metal substrates has been reported. The SERDP study also found that phenol acts as a co-solvent; phenol is probably the most effective co-solvent. Paint strippers formulated with acid and base activators are rarely accepted in the aerospace industry due to their corrosiveness to metal substrates. The products formulated with hydrogen peroxide have been reported to cause hydrogen embrittlement to certain metal parts. Other components are used in paint stripping formulations for the purposes that their names imply.
Methylene chloride based paint strippers provide superior performance; however, paint strippers that contain methylene chloride and phenol are regulated under various EPA and OSHA regulations. Environmental, Safety and Occupational Health (ESOH) compliant paint strippers, have been developed, marketed, and used, but these products have been found to have substantially lower striping rates as compared to methylene chloride based paint strippers. The poor performance of these paint strippers cause longer process time and high volatile organic compounds (VOCs) emission, which in turn substantially increases the maintenance cost especially in the aerospace industry.
Accordingly, there exists a need for high performance paint strippers, the performance of which could match that of methylene chloride based paint strippers. Such paint strippers would be formulated using chemicals that are safe for humans and the environment with no corrosive activators.
It is therefore an object of this invention to provide paint stripping compositions which provide superior performance but do not contain methylene chloride. It is another object of this invention to provide paint stripping compositions that are high in performance and compliant to the various EPA and OSHA regulations.
It is another object of this invention to provide a method and a chemical composition that does not contain phenol or methylene chloride and exhibits high performance in stripping paint from the substrate.